March 10, 2010 -- Stromectal -- a pill containing ivermectin, a drug used to
prevent heartworms in dogs -- kills head lice that are resistant to first-line
treatment better than malathion-based lotion.

The finding comes from a clinical trial sponsored by Merck, which makes the
parasite-killing pill.

When children bring home head lice, doctors usually recommend treatment with
one of several brands of pyrethroid-based products, such as Elimite, Acticin, Nix, A-200, Licide, Pronto, Pyrinyl Plus, Rid, and Tisit (although a
recent study showed that a louse-smothering product called
Ulesfia works well). But pyrethroid treatment fails if the head lice have
become resistant to the pesticide.

What should you try next? The Merck trial pitted Stromectal against an
alcohol-based product containing the powerful pesticide malathion (Prioderm
Top).

The study enrolled 812 head lice-infected people from 376 households in the
UK, Ireland, France, and Israel. Each household had already tried to get rid of
the pests with a pyrethroid product. All the people in each household had an
alcohol-based lotion applied to their heads by investigators -- and each
took a pill -- on two occasions seven days apart.

Half the people who got the lotion got the real product and half got a sham
product; half those getting pills got real Stromectal and half got an inactive
placebo.

On day 15, 95% of patients assigned to Stromectal and 85% of those assigned
to Prioderm Top were free of lice.

More patients preferred taking the pill to using the lotion. That isn't
surprising, as the lotion had to be left in the hair for 10 to 12 hours before
washing out.

There was one serious adverse event in each group. A 7-year-old girl had a
seizure six days after her first dose of Stromectal and was hospitalized, then
sent home with a prescription for an epilepsy drug. An 11-year-old girl had a
severe headache six days after first application of malathion lotion; she was
hospitalized overnight but recovered fully.

"Ivermectin may be a good alternative to malathion when topical insecticide
resistance is suspected," conclude study researchers Olivier Chosidow, MD, PhD,
of Pierre and Marie Curie University, Paris.

The Chosidow study appears in the March 11 issue of the New England
Journal of Medicine.